The present invention relates to reaction chambers used for processing semiconductor substrates, such as integrated circuit wafers, and specifically to improvements in the gas distribution system used in these reaction chambers.
Semiconductor processing includes deposition processes such as chemical vapor deposition (CVD) of metal, dielectric and semiconducting materials, etching of such layers, ashing of photoresist masking layers, etc. In the case of etching, plasma etching is conventionally used to etch metal, dielectric and semiconducting materials. A parallel plate plasma reactor typically includes a gas chamber including one or more baffles, a showerhead electrode through which etching gas passes, a pedestal supporting the silicon wafer on a bottom electrode, an RF power source, and a gas injection source for supplying gas to the gas chamber. Gas is ionized by the electrode to form plasma. The plasma etches the wafer supported below the showerhead electrode.
Showerhead electrodes for plasma processing of semiconductor substrates are disclosed in commonly assigned U.S. Pat. Nos. 5,074,456; 5,472,565; 5,534,751; and 5,569,356. Other showerhead electrode gas distribution systems are disclosed in U.S. Pat. Nos. 4,209,357; 4,263,088; 4,270,999; 4,297,162; 4,534,816; 4,579,618; 4,590,042; 4,593,540; 4,612,077; 4,780,169; 4,792,378; 4,820,371; 4,854,263; 5,006,220; 5,134,965; 5,494,713; 5,529,657; 5,593,540; 5,595,627; 5,614,055; 5,716,485; 5,746,875 and 5,888,907.
During the plasma etching process, plasma is formed above the masked surface of the wafer by adding large amounts of energy to a gas at relatively low pressure, ionizing the gas to form plasma. By adjusting the electrical potential of the wafer, charged species in the plasma can be directed to impinge perpendicularly upon the wafer, so that materials in unmasked regions of the wafer are removed.
It is desirable to evenly distribute the plasma over the surface of the wafer in order to obtain uniform etching rates over the entire surface of the wafer. Current gas distribution chamber designs include multiple baffles which are optimized to uniformly distribute etching gas to achieve the desired etching effect at the wafer. Conventional gas distribution designs include baffles having hundreds of openings or complex, difficult to manufacture geometries to ensure even distribution of etching gas to the backside of the showerhead electrode. Some attempts have been made to control gas flow by using a shaped electrode. However, manufacturing very pure silicon electrodes having complicated geometries is difficult and expensive. When etching large, twelve-inch (300 mm) wafers, controlling the process gas to create a uniform pressure distribution across the showerhead is even more difficult. The number of openings and baffles must be increased significantly to maintain uniform distribution of the etching gas. As the number of openings in the baffles increase and the number of baffles increase, the complexity and cost to manufacture such a gas distribution apparatus increase greatly.
U.S. Pat. No. 5,736,457 describes single and dual xe2x80x9cdamascenexe2x80x9d metallization processes. In the xe2x80x9csingle damascenexe2x80x9d approach, vias and conductors are formed in separate steps wherein a metallization pattern for either conductors or vias is etched into a dielectric layer, a metal layer is filled into the etched grooves or via holes in the dielectric layer, and the excess metal is removed by chemical mechanical planarization (CMP) or by an etch back process. In the xe2x80x9cdual damascenexe2x80x9d approach, the metallization patterns for the vias and conductors are etched in a dielectric layer and the etched grooves and via openings are filled with metal in a single metal filling and excess metal removal process.
From the foregoing it can be seen that as the size of semiconductor substrates increases, the ability to achieve uniform distribution of process gas above the substrates becomes more difficult. Accordingly, there is a need in the art for improvements in gas distribution systems. Further, to the extent that components of gas distribution systems are regularly replaced, it would be desirable if such components could be designed in a manner which facilitates economical manufacture thereof.
The present invention provides a gas distribution system which includes a contoured surface in a gas distribution chamber to achieve desired gas distribution delivered through a showerhead. Thus, the geometry of the contoured surface can be selected to optimize gas flow between the showerhead and the semiconductor substrate being processed.
The gas distribution system in accordance with the invention preferably includes a support body, a gas distribution chamber, a gas supply inlet, a showerhead and the contoured surface. The gas supply inlet supplies pressurized process gas into the gas distribution chamber and the showerhead is supported by the support body such that pressurized process gas in the gas distribution chamber applies pressure to a backside of the showerhead and passes through openings extending between the backside and an opposite side of the showerhead. The contoured surface is in the gas distribution chamber and is effective to provide a desired gas pressure distribution at the backside of the showerhead.
The contoured surface can be located on the support body or on a baffle plate located in the gas distribution chamber. For instance, the contoured surface can comprise a nonplanar upper and/or lower surface of the baffle plate or on a lower surface of the support body. The gas distribution chamber can comprise upper and/or lower plenums on opposite sides of the baffle plate or an open space between the contoured surface and the backside of the showerhead. The support body can include at least one coolant channel in which coolant can be circulated.
The gas inlet can open into various portions of the gas distribution chamber. For instance, the gas inlet can supply the process gas through a central opening in a planar surface of the support body facing the baffle plate in which case the baffle plate has a thickness which is larger in a central portion of the baffle plate and smaller at an outer portion of the baffle plate. Alternatively, the gas inlet can supply the process gas through an annular channel which opens into an outer region of the upper plenum in which case the baffle plate has a thickness which is smaller in a central portion thereof and larger at an outer portion thereof. The baffle plate can include uniformly sized openings extending between the upper and lower surfaces thereof, the openings having longer lengths either in the central portion of the baffle plate or in the outer portion of the baffle plate.
In the case where the contoured surface is a lower surface of the support body, the gas inlet can supply the process gas through a central opening in the lower surface and the open space can be smaller in a central region thereof and larger in an outer region thereof. Alternatively, the gas inlet can supply the process gas through an inlet which opens into an outer region of the open space in which case the showerhead can be spaced further from the contoured surface in the center region and closer to the contoured surface in the outer region.
The contoured surface can be an upper and/or lower nonplanar surface of a baffle section which is integral with the support body in which case the gas distribution chamber comprises an upper plenum above the baffle section and a lower plenum below the baffle section. In such a case, the upper plenum can be enclosed by an upper sidewall of the support body and a cover plate (which optionally can include one or more coolant channels) which seals against the upper sidewall and the lower plenum can be enclosed by a lower sidewall of the support body and the showerhead which seals against the lower sidewall.